The present invention relates to focused particle beam systems and methods for processing a workpiece, e.g., etching and imaging a cross-section of a workpiece.
Present focused ion beam (FIB) systems typically include an ion beam column oriented normal to the workpiece and a tilting work stage. Such systems can include an electron column offset from the normal to the workpiece. To image a cross-section of a workpiece using an ion column, existing systems etch a cavity in the workpiece and tilt the stage so that the ion beam can impinge on a side wall of the cavity.
Existing FIB systems which incorporate a tilting stage experience several problems. A tilting work stage, which is large relative to many of the other components of a FIB system, causes the system to be relatively bulky. Such a large bulk is disadvantageous because cleanroom fabrication space is expensive. A tilting work stage also causes an FIB system to be unstable because a tilting work stage can make an FIB system susceptible to low frequency vibration and gravity sag, as discussed further below. Disadvantageously, the vibration of and the changing configuration of a tilting work stage can interfere with the performance of a system component, such as a laser interferometer. Laser interferometry can be used to assist in accurate monitoring of the position of a workpiece.
Low frequency vibration can occur when a massive object, such as a tilting stage is supported by bearings and held steady with a mechanism that behaves like a spring. Low frequency vibration reduces resolution of a focused particle beam system by adding uncertainty in the determination of the location of the target point, i.e. where the ion beam interacts with the workpiece.
When a large as work stage assembly is tilted, gravity can bend components of the work stage assembly and the workpiece. Such bending is termed gravity sag. It is difficult to monitor gravity sap. Thus, gravity sag can lead to inaccuracy in determining the positions of the work stage and of the Workpiece. Such inaccuracy can reduce the resolution of a focused particle bear system.
Existing configurations of FIB systems restrict access to the workpiece by other elements, such as an optical microscope. Further, existing systems do not allow for optimization of the working distance of particular ion and electron columns. In existing configurations with a focused ion beam oriented normal to the workpiece and an electron beam offset with respect to the normal, one can not achieve working distances that optimize the characteristics, e.g., resolution and current density, of the ion and electron beams, because the work stage and the tip of the ion column and the tip of the electron column physically interfere with each other.
Accordingly, it is an object of the present invention to provide improved focused particle beam systems and methods for processing, e.g., etching and imaging a cross-section of a workpiece.
It is another object of the invention to reduce the footprint of a focused particle beam system.
It is another object of the invention to improve the stability of the work stage assembly of a focused particle beam system.
It is another object of the invention to improve the accuracy of a focused particle beam system.
It is another object of the invention to provide a focused particle beam system that allows for concurrent optimization of the working distances of a particle beam column and an electron beam column, the columns being oriented so that their target points are substantially coincident.
It is another object of the invention to provide a focused particle beam system that allows greater access to the workpiece by additional system elements such as an optical microscope.
Other objects of the invention will in part be obvious and in part will appear hereinafter.